What is the best way of making an MP4 from an image sequence (PNG)
Maybe the given answer is not specific enough for you. If you want an MP4 with best quality I would suggest (since you don't care about file size) to choose the following settings:

File Format: FFmpeg video
Container: MPEG-4
Video Codec: H.264
Output Quality: Perceptually lossless (with 'Lossless' I once had playback issues, might be because MP4 cannot be completely lossless, I'm satisfied with using 'High quality')
Encoding Speed: Slowest (should give best quality, but I see no advantage over 'Good')

Normally this should produce quite good results, although MP4 is not a lossless format it usually provides high quality along with a good compression i.e. small filesize.